Electronics Engineering (ELEX) Board Practice Exam

When Experimenter A uses a test charge-2q₀ to measure an electric field, how does the field compare to that found by Experimenter B?

1. It is much weaker.

2. It has a different direction.

3. It has the same magnitude and direction.

4. It is stronger but opposite in direction.

The correct answer is: It has the same magnitude and direction.

When Experimenter A uses a test charge of -2q₀ to measure an electric field, the fundamental principle is that the electric field is defined independently of the charge used for the measurement. The electric field at a point in space is a property of the source charges that generate the field and does not depend on the sign or magnitude of the test charge used to measure it. Therefore, regardless of whether Experimenter A uses a test charge of -2q₀ or some other charge to determine the electric field, both Experimenter A and Experimenter B are measuring the same electric field resulting from the same sources. As such, the electric field remains consistent in both magnitude and direction. This means that while the test charge affects the force experienced by it due to the electric field, it does not influence the characteristics of the electric field itself. Hence, both experimenters will find that the electric field they measure has the same magnitude and direction, confirming that the correct answer highlights this fundamental characteristic of electric fields.